The present disclosure relates to a light source, and particularly a seal for a light source of the type that uses a generally planar light emitting device such as an organic light emitting diode device or panel.
Organic light emitting diode devices, or OLED devices are generally known in the art. An OLED device typically includes one or more organic light emitting layer(s) disposed between electrodes. For example, first and second contacts, such as a cathode and a light transmissive anode are formed on a substrate. Light is emitted when current is applied across the cathode and anode. As a result of the electric current, electrons are injected into the organic layer from the cathode and holes may be injected into the organic layer from the anode. Electrons and holes generally travel through the organic layer until they recombine at a luminescent center, typically an organic molecule or polymer. The recombination process results in the emission of a light photon usually in the visible region of the electromagnetic spectrum.
The layers of an OLED are typically arranged so that the organic layers are disposed between the cathode and anode layers. As photons of light are generated and emitted, the photons move through the organic layer. Those that move toward the cathode, which generally comprises a metal, may be reflected back into the organic layer. Those photons that move through the organic layer to the light transmissive anode, and finally to the substrate, however, may be emitted from the OLED in the form of light energy. Some cathode materials may be light transmissive, and in some embodiments light may be emitted from the cathode layer, and therefore from the OLED device in a multi-directional manner. Thus, the OLED device has at least a cathode, organic, and anode layers. Of course, additional, optional layers may or may not be included in the light source structure.
Cathodes generally comprise a material having a low work function such that a relatively small voltage causes the emission of electrons. Commonly used materials include metals, such as gold, gallium, indium, manganese, calcium, tin, lead, aluminum, silver, magnesium, lithium, strontium, barium, zinc, zirconium, samarium, europium, and mixtures of alloys of any two or more thereof. On the other hand, the anode layer is generally comprised of a material having a high work function value, and these materials are known for use in the anode layer because they are generally light transmissive. Suitable materials include, but are not limited to, transparent conductive oxides such as indium tin oxide (ITO), aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO), indium doped zinc oxide, magnesium indium oxide, and nickel tungsten oxide; metals such as gold, aluminum, and nickel; conductive polymers such as poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT:PSS); and mixtures and combinations or alloys of any two or more thereof.
The OLED devices can be mounted on a rigid substrate such as glass or are generally flexible, i.e., are capable of being bent into a shape having a radius of curvature. In some instances, the OLED devices are coupled together to form a flexible, generally planar OLED panel comprised of one or more OLED devices. Such a panel has a large surface area of light emission.
Oxygen and moisture are particularly deleterious to an OLED structure. The intrusion of oxygen or moisture into the OLED device results in dark spots, decreased illumination, etc. It is important, therefore, to create a hermetic package around the OLED panel to limit the potential for ingress of oxygen, moisture, etc. A particular area of concern is along the perimeter edge of the OLED device or panel where laminate edges of adjacent layers of the structure of the OLED device are potentially exposed and possibly subject to oxygen and/or moisture ingress.
Presently, a barrier material is provided on one or both of the first or upper and second or lower surfaces of the OLED device or panel. Accommodations are made to seal the peripheral portions of the first and second surfaces in an effort to prevent moisture and/or oxygen from reaching the functional materials of the OLED device. This often requires compatibility of the barrier materials with the materials of the OLED device in an effort to seal the first and second surfaces adjacent the edge.
A need exists to provide an effective edge seal to maximize illumination efficiency, and increase useful life of an OLED device or panel.